Air ionizers have one or more sharply pointed electrodes to which high voltage is applied. The resulting intense electrical field in the vicinity of the sharp points dissociates nearby air molecules into positive and negative ions. Ions having a polarity opposite to that of the high voltage are attracted to the electrode and neutralized, Ions of the same polarity as the high voltage are repelled by the electrode and by each other and disperse outwardly from the ionizer into the surrounding atmosphere.
Air ionizers of the above described kind were originally designed primarily for producing beneficial effects in people who breathe the air and/or for removing particulate pollutants, such as dust, smoke or the like, from the air. Negative air ions in particular are physiologically beneficial while ions of either polarity remove pollutants by imparting an electrical charge to such particles. The charged particles then deposit on nearby walls or other objects as a result of electrostatic attraction.
The ion output rate of such apparatus is basically determined by the magnitude of the high voltage and the area and configuration of the electrode ion output regulation in early ionizers was usually confined to use of a voltage regulator in the high voltage generator power supply. The regulator in effect maintained the high voltage on the electrode at a fixed or in some cases selectable level. This does not assure that ion output will remain constant over a period of time. The electrode deteriorates and changes configuration as a result of the corona discharge which occurs at the point or points of the electrode. This typically causes a gradual decrease in the rate of ion production. Deterioration of other components can also alter ion output.
A more precise regulation of ion output is desirable under some circumstances. Most notably, air ionizers have been found to be a highly effective means for suppressing the build-up of electrostatic charges on objects in a room. Objects and people tend to acquire electrostatic charges ranging up to several thousand volts as a result of movement and the accompanying friction, from inductive effects and by discharges from other objects. Sudden discharges of such static electricity can be discomforting to people and can damage a variety of devices and articles. Computers and recording equipment, among many other examples, can be disrupted by electrostatic discharges.
Elaborate precautions must be taken in so called clean rooms in which semiconducting electronic components are manufactured. Electrostatic discharges can destroy the minute conductive paths in microcircuits. Static charges on semiconductor wafers or the like also attract damaging dust particles and other contaminants. Maintaininq a high level of air ions in the region around such products is one of the more effective techniques for minimizing damage as an electrostatic charge of given polarity is neutralized by charge exchange with air ions of opposite polarity.
Air ionizing apparatus for suppressing static electricity accumulations are usually designed to produce both positive and negative ions. The charge accumulations on objects can be of either polarity. This creates a need for precise regulation of the output of ions of each type.
The desired rates of production of positive and negative ions may be equal or may have some other ratio depending on the static charge accumulating tendencies of the particular clean room. In either case, a change in the ratio of positive and negative ion outputs brought about by electrode deterioration or other causes can have adverse effects. The ionizing apparatus may then tend to impart electrostatic charge to objects rather than suppressing such charges. A change in the combined output rates of the positive and negative ions from such causes may also have adverse effects.
The rate of air ion generation at a particular electrode can be controlled by adjusting the magnitude of the high voltage that is applied to the electrode. Higher voltage increases ion output and lowered voltage decreases output. Such use of voltage control to maintain a desired rate of ion production requires monitoring of ion output to detect changes.
Prior monitoring systems for this purpose use ion sensing devices which are situated away from the ionizing electrodes and which are usually located in the region of the objects on which static charge is to be suppressed. The ion sensor transmits a signal indicative of changes of ion content in the adjacent air. The signal may be read on a meter to enable manual adjustment of electrode voltage or may be fed back to a servo control at the high voltage generator for automatic adjustment of voltage.
Ion sensor controlled systems have significant limitations and disadvantages. Such sensors pick up environmental noise and have a limited spatial range. Ion sensors are also costly. These are highly significant disadvantages in large area systems which may include an array of many spaced apart ionizing electrodes. A number of sensors are needed to detect imbalances of positive and negative ions or changes in total ion content throughout a room. Ideally such a system would include one air ion sensor for each ionizing electrode but the high cost of the devices has made this impractical in many cases.
Usage of air ionizing apparatus would be greatly facilitated by a construction which inherently maintains a desired high concentration of ions in the nearby atmosphere and a desired ratio of negative to positive ions and which does so in an accurate and reliable manner and without excessive costs.